This disclosure generally relates to systems and methods for repairing structures comprised of composite materials, and in particular, to methods and systems for effecting such repairs with limited resources and time.
The use of structures comprised of composite materials (such as carbon fiber/epoxy composite material) has grown in popularity, particularly in such applications as aircraft structures, where benefits include increased strength and rigidity, reduced weight and reduced parts count. When damaged, however, composite structures often undergo extensive repair work. If performed on an aircraft, the repair work may ground the aircraft, thereby adding significantly to the support costs of the aircraft. Current maintenance procedures frequently cause the damaged component to be removed and replaced. If performed on an aircraft, the repair work may need to be completed before the aircraft can resume flying.
Commercial airlines today do not have the ability to repair structural damage to an aircraft's composite structures without severely delaying or canceling the aircraft's next flight. Short domestic flights may have only 30-60 minutes of time at the gate whereas longer and international flights may have 60-90 minutes. The Commercial Airline Composite Repair Committee, an international consortium of airlines, OEMs, and suppliers, reports, however, that the average composite repair permitted in the Structural Repair Manuals takes approximately 15 hours to complete. In most cases, flight cancellations occur when a composite repair is performed at the flight line. Removing an airplane from revenue service in order to repair a damaged composite structure costs the operator the labor to repair the structure and the adjustments to its flight schedules. It may also cause passenger dissatisfaction.
Damage to composite material can be repaired using any one of a number of known methodologies. Many of these known repair techniques involve clean-up of the damaged site followed by the installation of a repair patch made of composite material. Current state-of-the-art bonded patches for composite structure are relatively complicated and time-consuming to apply. They also are not designed to have bond strength verified using non-destructive evaluation (NDE) methods. Patch repairs cannot generally be verified because of the potential of kissing bonds that hold no load but are often invisible to current NDE methods. (As used herein, the term “disbond” refers to a separation of composite material from another material to which it has been adhesively bonded. A disbond that is tight with no bond strength or weakly bonded is referred to herein as a “kissing bond”.) Typically, just bond line defects or voids can be identified. Traditional composite repair patches do not have visual indication of adhesive continuity or pressure application. This drawback has severely limited the use of bonded patches on aircraft, since their performance cannot be verified in any significant way.
Composite patch repair methods that can provide visual or NDE verification of the structural integrity of the repair would be a marked improvement over the above-described repair techniques.